1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus capable of adjusting print density.
2. Description of the Related Art
Image forming apparatuses such as an electrophotographic printer use an electrophotographic image forming process including steps of charging, exposing, developing, transferring, and fixing. A charging roller charges the surface of a photoconductive drum uniformly. An exposing unit employs a light source such as LEDs or a laser, and selectively illuminates the charged surface of the photoconductive drum to form an electrostatic latent image. The electrostatic latent image is then developed with charged toner into a toner image. The toner image is transferred onto a print medium, and finally fused by a fixing unit into a permanent image. The density of toner images may change with time and environmental changes. Additionally, toner may adhere to areas in which no electrostatic latent image is formed, leading to soiling of the surface of the photoconductive drum. One conventional way of solving this type of soiling of the photoconductive drum is to adjust the charging voltage that charges the surface of the photoconductive drum.
However, while soiling of the photoconductive drum may be prevented by adjusting the charging voltage, soiling of the printed images due to abnormally charged toner may be difficult to prevent.